1. Field of the Invention
The invention relates to adhesive materials such as tapes that provide a dry and reusable medium for adhering two surfaces together.
2. Description of Related Art
Much of thermal management involves the transfer of heat from one element to another. While individual elements might have very high conductance, the heat transfer rate between contact surfaces of the two elements can limit overall performance of the thermal control system. Similarly, the strength of an adhesive bond formed between the two elements is often dependent on the contacting surfaces. The heat transfer rate and adhesive strength between the two elements can improve by maximizing the contact region between the two elements.
Existing methods of bonding include brazing, soldering, gluing, bolting, taping, sewing, zippering, and use of Velcro® fasteners. Desirable properties include high strength of attachment, easy removability, reliability, and reusability. Other considerations include chemical compatibility, outgassing, and mass. Brazing and gluing with adhesive is strong, but not reusable nor easily removable. Bolts can be heavy and require special fixturing for attaching. Tape is not very strong, tends to leave a residue, and loses its sticking ability with use. It does not work well in wet environments.
A different form of adhesive is found in a foot of a Tokay gecko. The foot includes a structure which allows the gecko to run over glass ceilings or climb wet glass walls. The toes of the Tokay gecko have pads consisting of thousands of 5 um-diameter keratinous fibers (called setae). The ends of the setae split into hundreds of 100-nm diameter fibrils. Each nanofibril terminates in an ellipsoidal structure called a “spatula.” Each spatula has a diameter ranging from 200–500 nm. The adhesive force of a single seta against Si was measured to be 200 μN (20 mg). It has been hypothesized that van der Waal forces are responsible for the gecko's amazing ability to climb up smooth vertical surfaces. If utilized to full capacity, the 100 mm2 area of a gecko's foot, consisting of 500,000 such setae, should then be able to produce 100 N (10 kg) of adhesive force. The corresponding effective adhesive strength is 106 MPa (15,000 psi). This adhesive strength is well suited for many applications. The micron-size setae serve as a compliant support which conforms to the surface to allow the nanometer-sized tips (themselves compliant on a small scale) to make intimate contact with the surface.
A manufactured adhesive that could provide the adhesion properties of the gecko foot is desirable. Such an adhesive would be compliant and could stick by intermolecular (van der Waals) forces resulting from its intimate contact with the surface. Such an adhesive would provide broad utility as an adhesive or attachment mechanism. The adhesive could be strong, dry, removable, reusable, and lightweight, combining many of the most desirable properties of the gecko foot. Such an adhesive may also have enhanced thermal and/or electrical conductance, providing an effective thermal/electrical interface with a built-in attach mechanism that is strong, removable, and reusable.